The present invention relates to an electromagnetic actuator.
It is well known to utilize electromagnetic actuators, commonly referred to as solenoids, to control the operation of ancillary devices such as hydraulic valves. The principle of operation is well known and utilizes the magnetic field produced by a coil to cause displacement of a magnetizable core.
One such arrangement is shown in U.S. Pat. No. 5,513,832 to Becker in which a hydraulic valve is controlled by an armature mounted within a coil. The armature includes a magnetizable core supported on a central pin. The pin is guided for movement at one end in a conventional bearing. At the opposite end, a fluid-tight diaphragm is provided that includes a plate spring to provide a return force on the armature.
The accurate control of the ancillary device depends upon the repeatability of the response to a given input signal and the proportionality of that response. As such, the mechanical systems utilized to support an armature within the actuator have a significant effect upon the performance of the actuator and the device upon which it is acting. The coil not only imparts axial forces to the armature but also imparts radial forces. Conventional bushings of the type shown in the Becker patent are therefore susceptible to increased friction forces, particularly as the actuator wears, and radial misalignment that affects the proportionality of the response from given inputs.
It is therefore an object of the present invention to provide an actuator in which the above disadvantages are obviated or mitigated.